The bag cell neurons of the marine ophistobranch mollusk Aplysia, synthesize and release, when active, a number of polypeptides and peptides. One of these polypeptides, approximately pl 9, m.w. 6000, induces egg-laving and correlated behavior when injected into recipients. This neuropolypeptide, egg-laying hormone (ELH), has been purified and partially sequenced and is known to have direct effects on the central nervous system of Aplysia. We propose to generate antibodies to ELH for a variety of biochemical and physiological experiments: With ELH antibody and radioiodinated ELH, we can quantitate levels of ELH in blood (during mating), during in vitro discharge of bag cells (BCs) and while isolating ELH from BC clusters. With indirect fluorescence we can establish, by immunocytochemistry, whether ELH is synthesized in all BCs and how this changes with sexual maturity. With radioiodinated ELH we can begin to probe where the various target organs and receptors for ELH are localized. The BC neurons in each cluster discharge synchronously on synaptic activation in vitro and afterdischarge for approximately 30 minutes (at 14 degrees C) after synaptic activation. Following such an afterdischarge, the BC neurons refractory, for generating another long afterdischarge, for several hours. We propose to investigate the mechanisms by which the afterdischarge and subsequent refractoriness are generated using electrophysiological, pharmacological and biochemical techniques. Our present evidence indicates an increase in cAMP during the early stage of afterdischarge and the removal of refractoriness for afterdischarge by phosphodiesterase inhibitors.